[Equest-users] Fan usage - PTHP vs PSZ

Singhal, Harshul HSinghal at ThorntonTomasetti.com
Mon Mar 16 07:19:52 PDT 2015

Hello forum,

Our team received a note from our LEED reviewers that our equivalent full load hours (EFLH) in our baseline model were less than 8760, despite the ASHRAE 90.1 requirements that fans be run at constant speed 24 hours per day for multifamily occupancy type.  Our baseline system type is PTHP.  When we plot hourly fan energy usage for the building, usage varies hourly and loosely follows the profile of the outside air temperature.  The EFLH is approximately 7517 hours (88%).   When we switch the system to 'packaged single-zone heat pump' from 'packaged terminal heat pump' EFLH becomes 8760.  This seems to indicate that the lower EFLH of our baseline model is somehow associated with the system type, however our team can't seem to figure out what characteristic of a PTHP causes fan energy to change hourly despite the 'constant speed' designation.  Does anyone have any insight as to why PTHP EFLH would be below 8760 while packaged single-zone heat pump would not be?  Thanks for any insight you might have.


[cid:image002.jpg at 01D05CF2.73106640]

Harshul Singhal, LEED AP BD+C
Project Consultant
Thornton Tomasetti
386 Fore Street, Suite 401
Portland, ME  04101
T +  F +
D +
HSinghal at ThorntonTomasetti.com


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